The present disclosure relates to an out-of-head localization processing apparatus and an out-of-head localization processing method.
As one of the sound field reproduction techniques, there is an “out-of-head localization headphone technique” that generates a sound field as if sound is reproduced by speakers even when the sound is actually reproduced by headphones. The out-of-head localization headphone technique uses, for example, the head-related transfer characteristics of a listener (spatial transfer characteristics from 2ch virtual speakers placed in front of the listener to his/her left and right ears, respectively) and ear canal transfer characteristics of the listener (transfer characteristics from right and left diaphragms of headphones to the listener's ear canals, respectively).
In out-of-head localization reproduction, measurement signals (impulse sound etc.) output from two-channel (hereinafter referred to as ch) speakers are recorded by microphones placed in the listener's ears. Then, head-related transfer characteristics are calculated from impulse responses, and filters are created. The out-of-head localization reproduction can be achieved by convolving the created filters with 2ch music signals.
It is possible to accurately measure characteristics by disposing microphones in ears (preferably in entrances of ear canals) of a listener. However, measurement which is performed after disposing microphones at entrances of ear canals of a listener is complicated. Therefore, Patent Literature 1 (Japanese Unexamined Patent Application Publication No. 2002-135898) discloses a method for measuring transfer characteristics by using headphones equipped with built-in microphones.
In Patent Literature 1, coefficients are successively updated by using adaptive signal processing so that signals of microphones disposed on inner sides of the headphones have desired characteristics. By doing so, desired target characteristics can be obtained. Note that the target characteristics are, for example, transfer characteristics that are obtained near both ears when a center sound source is placed in front of a user.